A college student has helped break a code that's stumped archaeologists for centuries. The Incas did not have a written language. Instead, they communicated using a system of knots in colored strings called khipus. Until now, people had a very limited understanding of what those knots were communicating.

Manny Medrano is a junior at Harvard University, and he's here to tell us how he cracked the code. Welcome, and congratulations on the breakthrough.

MANNY MEDRANO: Thank you very much for the opportunity to speak with you.

SHAPIRO: Will you just start by describing what one of these cords looks like?

MEDRANO: Picture a horizontal string from which up to hundreds of other strings hang down like icicles. What we're looking at is hundreds of cords, each with a series of knots which appear similar to a stretched-out string mop is the best mental image I could try to conjure.

SHAPIRO: Looking at images of them, it actually looks like a work of art. But it's there to communicate something. What was your insight about what it is communicating?

MEDRANO: Well, it's been established for about a hundred years, actually, that these artifacts - and there's about a thousand of them that exist still today from the time of the Inca empire - we've known for about a hundred years that many of these encode numerical information, everything from census documents to tax information, just like our modern documents do today. But the change in tide that's been happening really in recent years and the reason why this is still an exciting field of study for the future is perhaps - the idea is that these artifacts really went past just an abacus or just an Excel spreadsheet and may have contained narrative information.

SHAPIRO: Tell me about the moment you had the insight. Was it the stereotypical eureka, aha, I've got it?

MEDRANO: Well, it was during spring break. And I had stayed behind while my roommates were visiting family back at home. And comparing these Excel spreadsheets where we have recorded the data from these six artifacts, these six khipus, with the text of this Spanish census document, a coincidence arose that seemed too strong to be random.

SHAPIRO: What was the coincidence? Can you explain it in a way that we could understand?

MEDRANO: Sure. The coincidence that we found is if you were to add up the names of all these villagers - a list of 132 of them, all with different first names - we have Joses (ph) and Felipes (ph) and this group of villagers. The thought is if I were making a census khipu, if I were knotting strings to encode the information of these villagers, how would I do it? And the first instinct was assign a different color to the Joses and then a different color to the Felipes. And each of those color assignments, if we added up all the strings that were light brown and all the strings that were dark brown, those sums actually equaled the numbers of different first names. And what that points us toward is a match between usage of color and categorization of these taxpayers into buckets.

SHAPIRO: There were other cultures from this time period that had written languages. This is an actually tactile language that you can touch instead of reading. What's the significance of that?

MEDRANO: The khipus are incredible because they compel us to interpret history in multiple dimensions. South America's the only continent besides Antarctica on which no civilization invented a system of graphical writing for over 10,000 years after the first people arrived. And what that means in the course of history is that the Incas are often defined by what they lack and with a despite clause. In other words, this civilization who never invented the wheel, never invented markets and lacked a system of graphical writing are often defined as never having stumbled upon the wonders of civilization. And this project is aimed at reversing that incorrect narrative.

SHAPIRO: Manny Medrano is a junior at Harvard, and his research into the Incan code with anthropology professor Gary Urton will be published next month in the journal Ethnohistory. Manny, thanks so much.